As a transistor forming a power amplifier module such as that in a mobile terminal, a heterojunction bipolar transistor (HTB) is used. This type of bipolar transistor has a mesa structure.
In order to prevent the occurrence of failures in a semiconductor element such as a bipolar transistor, for example, since the semiconductor element is damaged or malfunctions by electrostatic discharge, ESD (Electro Static Discharge) protection elements are formed in a semiconductor device. An example of ESD protection elements is diodes.
Concerning diodes used as ESD protection elements for a bipolar transistor, because of their electrical characteristics such as the ability to withstand voltage and the resistance, plural diodes are connected in series with each other. One of the patterns (layouts) concerning the arrangement of the plural diodes is the one in which a predetermined number of diodes JD are linearly connected to each other in one direction, as shown in FIG. 19.
In a semiconductor device 101 having this pattern, among the linearly connected plural diodes JD, an input terminal 108 is connected to a P-type region of a diode positioned at one end, while an output terminal 109 is connected to an N-type region of a diode JD positioned at the other end.
Examples of patent documents which disclose didoes used as ESD protection elements are Japanese Unexamined Patent Application Publication No. 2002-217374 and WO2001-18865.